Walmart is offering U.S. consumers a free Nokia Lumia 710 smartphone when they sign up for a two-year service commitment with T-Mobile. By contrast, T-Mobile is selling the same Windows Phone handset at a post-rebate price of $50 in exchange for a two-year service commitment.

"Walmart and other national retailers are able to set their own pricing for T-Mobile products," a T-Mobile spokesperson said.

To help drive sales, T-Mobile is also pitching an "unlimited" data voice and texting plan, though this two-line family plan also has a 2GB monthly data cap.

"After the 2 GB allotment of data is reached, the customer will be notified via a free text message from T-Mobile that they have exceeded that monthly threshold," a T-Mobile spokesperson said in a Monday e-mail. "However, the customer may continue to use the current plan with reduced data speeds for the remainder of the month."

Lumia Device Comparisons

T-Mobile's Lumia 710 and AT&T's coming Lumia 900 are similar in several respects. For example, both handsets are powered by Microsoft's Windows Phone 7.5 platform, also known as Mango, and both feature displays that are protected by scratch resistant Gorilla Glass.

Under the hood, the two handsets run Qualcomm's 1.4 GHz Snapdragon processor and 512-megabytes of RAM, together with Wi-Fi (802.11b/g/n) and Bluetooth (2.1 +EDR) radios. However, the Lumia 900 will ship with 16 GB of data storage, compared with the 8 GB offered by the Lumia 710.

On the software side, both Nokia smartphones offer an interactive mobile gaming experience through Microsoft's Xbox Live service. In addition, both models provide access to Microsoft's entire range of online services as well as instant access to Facebook, Twitter, LinkedIn, e-mail, Chat, and SMS over the handset's People Hub.

Still, AT&T's Mango-powered Lumia 900 will feature a number of other design improvements not found on T-Mobile's Lumia 710, such as 4G LTE connectivity. The AT&T handset also will feature a big and bright 4.3-inch AMOLED display, whereas the Lumia 710 is equipped with a smaller 3.7-inch screen based on old TFT technology.

Under the breakup terms of its unsuccessful merger deal with AT&T, T-Mobile will receive a large package of advanced wireless spectrum in 128 cellular market areas across the United States, including 12 out of the nation's top 20 metropolitan markets.

Meanwhile, the wireless carrier is doubling the speed of its existing high-speed packet access plus network by moving from HSPA+ 21 to HSPA+ 42.

"Our 4G network is better than ever heading into 2012," said T-Mobile USA Chief Technology Officer Neville Ray. "HSPA+ will continue to deliver a competitive mobile broadband experience for our customers in the coming years as we evaluate our options for continued investment and evolution of our 4G network."

On the other hand, advanced mobile devices such as Nokia's Lumia 900 provide AT&T subscribers with access to new 4G LTE connections in those market areas where T-Mobile's rival is rolling out its new super-fast network. Still, T-Mobile believes that its current 4G network is fast enough right now to give the carrier some breathing room to develop its own next generation system.